The present invention concerns apparatus for controlling a vacuum-actuated device which provides a continual adjustment of the closing limit of a carburetor throttle valve of a motor vehicle engine; specifically, an internal combustion engine of the type in which a fuel-air mixture is supplied to the engine intake manifold. More particularly, the invention relates to apparatus for controlling a valve, such as a solenoid valve, arranged in the vacuum line extending from the intake pipe or manifold of the engine to this closing adjustment mechanism.
In order to decrease the emission of noxious substances during deceleration operation of motor vehicle (automobile) engines of the aforementioned type, a technique is known whereby the carburetor throttle valve is opened sufficiently widely, during this operating state, to supply an adequate quantity of air for combustion of the fuel which reaches the combustion chambers. This throttle valve position is customarily achieved by means of a vacuum-actuated device that receives vacuum through a connecting line from the intake pipe of the engine.
A vacuum of approximately 370 mm Hg in the intake pipe is normally required for optimal combustion during deceleration operation of an automobile engine. However, this vacuum level is less than the normal idling vacuum of approximately 400 mm Hg so that, during idling, the throttle valve-controlling vacuum actuated device would tend to open the throttle slightly, and thereby increase the speed of the engine, if measures were not taken to prevent this from occurring. It is known from the German patent publication (DOS) No. 2,046,436 to cut off the intake vacuum to the vacuum-actuated device at low vehicle speeds. To this end the vacuum line leading from the intake pipe to the vacuum-actuated device is provided with an electromagnetically-actuated (solenoid) control valve which is switched as a function of vehicle speed by a relatively costly electronic circuit. In addition to the high cost of this arrangement, this known device has the disadvantage that, during operation of the vehicle at speeds close to the speed at which the control valve is switched, an undesirable multiplicity of control pulses act on the throttle flap due to repeated switching of the control valve.
Thus, it is an object of the present invention to provide control apparatus of the type described above which is distinguished by low manufacturing cost and faultless operation. It is assumed in this connection that the intake pipe vacuum is to be disconnected from the closing adjustment mechanism at defined operating states of the vehicle; namely, when the vehicle is standing with the engine switched off, when the vehicle is idling with the transmission in neutral, when the vehicle is operated in first gear, and when the vehicle clutch is disengaged.